The present invention relates to mechanical transmissions and more particularly to a multi-function wheel transmission for wheelchairs and the like.
Conventional wheelchairs provide necessary mobility for the disabled. Manually driven chairs have an advantage in that they provide the opportunity for some physical exercise. Nevertheless, manual chairs are limiting to the user because pathways must be relatively flat for easy and safe locomotion. Sloping surfaces are more difficult to roll a chair up than a flat surface and a downward slope can be dangerous if the user loses control of the wheels. Substantial strength and dexterity are required for locomotion on sloping surfaces. A braking mechanism must be included for safety.
Electric wheelchairs give mobility to the disabled for a wide variety of terrain. But electric chairs can be expensive and bulky and deprive the user of physical exercise. Manually driven wheelchairs provide a lesser degree of mobility but are lighter, less expensive and can provide a good opportunity for controlled exercise.
It is therefore an object of the present invention to provide a new multi-speed transmission for use in a mobility enhancing vehicle, such as a wheelchair.
It is another object of the present invention to provide a new braking mechanism in a mobility vehicle.
It is yet another object of the present invention to provide a new multi-function transmission for use in a mobility enhancing vehicle which has a braking mechanism for safety.
The present invention relates to mechanical transmissions and more particularly to a multi-function wheel transmission for wheelchairs and other mobility enhancing vehicles. In an embodiment of the present invention, a selectable xe2x80x9clow gearxe2x80x9d is provided for going up a hill. Use of this embodiment in a wheelchair lessens user anxiety by inherently providing a safety mechanism that prevents runaway on a ramped or sloped surface; this innovation provides increased mechanical advantage while also having inherent safety braking. The result is enhanced confidence and mobility both for an average user and for a hard driving athlete in a manual wheelchair.
A preferred embodiment of the invention is built into each wheel and has two modes. The user selects the mode by using a braking lever. When the brake is off the wheelchair operates like a conventional manual chair. The user strokes the drive rim to drive the chair. This is the normal mode.
When the brake is set, then the wheelchair acts as if the brake is on as in the conventional manner. But if the drive rim is stroked then the wheelchair is propelled via the torque-amplifying hub transmission of the invention. The result is that the wheelchair can traverse a steep incline or decline and as soon as the user stops driving the rim, the wheelchair safely comes to a stop. Now threatening hills and steep ramps can be safely traversed at any rate, slow or fast, even with a rest stop in the middle. With the hub transmission engaged, there can be no runaway. This is the speed converter mode.
In use, just like using low gear on a bike, compared to a conventional wheelchair trying to go up a steep incline, the hub makes it much easier on the musclesxe2x80x94and feels itxe2x80x94because of it is a torque amplifier. The chair is used in the convention manner when rolling on level ground. But when easier propulsion or self-braking is important, the user puts the brakes on and then uses the drive rim through the hub for propulsion.
The mechanical advantage in the hub can be so effective as to make it possible for a user to propel up an incline that heretofore was considered insurmountable. Or this mechanical advantage may benefit an aged or enfeebled user even on a level surface. In any event, the hub invention can extend the range of mobility of the conventional manual wheelchair and its user. The present invention results in increased mobility in an easy to use and cost-effective wheel design for any wheelchair, new or retrofit.
Since athletic events for the wheelchair-bound are becoming more popular, there is a variation on the above theme that is part of the invention. Rather than a speed reducer hub, we implement a speed increaser hub for a racing wheelchair, where the user can select a high-speed overdrive mode to increase the top-end speed achievable by the racer. In this case the speed increaser is used for much like a high gear in an automobile. The shift mechanism for the wheels can be tied together to be activated simultaneously and on-the-fly. There is no auto-braking feature in this embodiment.
In a preferred embodiment of the invention, each wheel has a single drive rim that performs two functions. A brake assembly is provided to manually shift between two modes: a 1:1 conventional drive mode and a n:1 non-backdrivable self-braking mode. In the latter mode, rotary motion applied to the rim is translated via a hub assembly to drive the wheel via a non-backdrivable torque amplifying speed reducer. In this aspect of the invention, the wheel brake is automatically applied to the wheel to stop unwanted motion, unless the drive rim is rotated. In another aspect of the invention, when the brake is disengaged, per wheel, rotation of the drive rim drives the wheel in a conventional manner.
In a preferred embodiment of the present invention rotary motion applied to the drive rim is translated via a conjugate pair of devices rotatable about a common axis, and a ball or roller type translating arrangement, interposed between the conjugate pair about the common axis, including a slotted retainer device, forming a torque amplifying non-backdrivable speed reducer, to drive the wheel. When the drive rim is not being rotated and the brake is engaged, then the wheel is automatically prevented from rolling to stop unwanted motion unless the drive rim is intentionally driven. When the brake is disengaged, rotation of the drive rim drives the wheel in a conventional manner.
It will now be appreciated that a multi-motion transmission is disclosed, having an input, reaction system, housing, and output. In an embodiment of the invention, a first of these items connects to a second one to form a first mode of operation, and the first of the items decouples from the second one and couples to a third item to form a second mode of operation. Speed conversion apparatus is provided and the input is rotatably coupled to the output via the speed conversion apparatus in one mode of operation, wherein the input has a first rate of motion and the output has a second rate of motion.
Clutching provides for selectively switching between the first mode and second mode, and selectively engages one of the said items to other ones of said items, for provision of the first rate of motion in one mode and a second rate of motion in the other said mode. In a preferred embodiment, this clutching action enables a braking function in one mode, where the hub transmission includes a non-backdrivable speed reducer. In another embodiment, the speed conversion apparatus is a backdrivable speed increaser.
Preferably the transmission of the invention includes a conjugate pair of devices nested concentrically about a common axis, where a first of the pair of the devices is an inner cam gear and the second is an outer cam gear. The cam gears may include rotary wavy tracks. A slotted part is nested between the two can gears and has a plurality of slots for receipt of interacting elements (balls or rollers). Where the transmission has a housing, such as a wheelchair frame, the input and output are selectively rotatable relative to the housing, wherein a shifting part engages one of the devices for switching between a first mode and a second mode of operation, such as for switching between 1:1 and n:1 operation.